Error concealment system using dropout severity information for selection of concealment method

Abstract

An error concealment system for a digital video signal uses different methods of concealment in accordance with the severity of the error. An adaptive estimate (horizontal or vertical average) is used if all pixels need for such an estimate are valid. If not, a four pixel average is used. If that is not possible a vertical average is used, and finally a horizontal average is used. If the error is very severe, then a line store provides the last valid line.

What is claimed is: 
     
       1. Apparatus for concealing an erroneous sample of a sampled digital video signal, said apparatus comprising: a plurality of estimate generating means for generating a plurality of estimates of the value of said erroneous sample by averaging samples proximate said erroneous sample, comprising an adaptive average estimate generator for generating an adaptive average estimate, a four-sample average estimate generator for generating a four-sample average estimate, a vertical average estimate generator for generating a vertical average estimate, and a horizontal average estimate generator for generating a horizontal average estimate;   error determining means including an error detector responsive to said sampled digital video signal for providing defect signals indicating which of said samples proximate said erroneous sample are defective;   logic gate means having a plurality of inputs coupled to receive said defect signals for providing a control signal responsive to said defect signals; and   selecting means having a plurality of inputs coupled to receive said plurality of estimates of the value of said erroneous sample, and also having an output terminal to which a selected one of said plurality of estimates of the value of said erroneous sample is coupled, and having a control input coupled to receive said control signal and being responsive to said control signal for coupling to said output terminal said adaptive average when said control signal indicates that none of said samples proximate said erroneous sample are defective samples, said four-sample average when said control signal indicates that some of said samples proximate said erroneous sample are defective but none of said samples proximate said erroneous sample which are both horizontally and vertically adjacent said erroneous sample are defective, said vertical average when said control signal indicates that some of said samples proximate said erroneous sample are defective but none of the vertically adjacent samples proximate said erroneous sample are defective, and said horizontal average when said control signal indicates that some of said samples proximate said erroneous sample are defective but none of the horizontally adjacent samples proximate said erroneous sample are defective.   
     
     
       2. Apparatus for concealing an erroneous sample of a sampled digital video signal, said apparatus comprising: a plurality of estimate generating means for generating from signal samples proximate said erroneous sample (a) a four-sample average estimate (b) a vertical average estimate, (c) a horizontal average estimate, and (d) an adaptive estimate of the value of said erroneous sample, wherein said adaptive average estimate generating means includes means for computing the amplitude difference between horizontally adjacent samples in at least one line adjacent the line including said erroneous sample and providing said horizontal average estimate if said amplitude difference is less than a selected amount and said vertical average estimate if said amplitude difference is greater than said selected amount;   determining means including a defect detector responsive to said sampled digital video signal for providing defect flag signals indicative of which of said samples proximate said erroneous sample are defective samples;   logic gate means having a plurality of inputs coupled to receive said defect flag signals for generating a control signal; and   selecting means having a plurality of inputs coupled to receive said four-sample average estimate, said vertical average estimate, said horizontal average estimate, and said adaptive average estimate of said value of said erroneous sample, said selecting means also having a control input coupled to receive said control signal, for coupling to an output terminal of said selecting means under the control of said control signal (a) said adaptive average when said control signal indicates that none of said samples proximate said erroneous sample are defective, (b) said four-sample average when said control signal indicates that some of said samples proximate said erroneous sample are defective but none of said samples proximate said erroneous samples which are vertically and horizontally adjacent said erroneous sample are defective; (c) said vertical average when said control signal indicates that at least some of said samples proximate said erroneous sample which are diagonally and horizontally adjacent said erroneous sample are defective but that none of said samples proximate said erroneous sample which are vertically adjacent said erroneous sample are defective; and (d) said horizontal average when said control signal indicates that at least some of said proximate samples which are diagonally and horizontally adjacent said erroneous sample are defective but none of the samples horizontally adjacent said erroneous sample are defective.   
     
     
       3. Apparatus for concealing an erroneous sample of a sampled video signal from a source of sampled video signal, said apparatus comprising: first average estimate generating means coupled to said source of sampled video signal for generating a first estimate of the value of said erroneous sample by averaging the values of first proximate samples located adjacent said erroneous sample in a first direction;   second average estimate generating means coupled to said source of sampled video signal for generating a second estimate of the value of said erroneous sample by averaging the value of second proximate samples located adjacent said erroneous sample in a second direction;   control signal generating means coupled to said source of sampled video signal for generating a control signal indicative of the presence of a defect in one of said first and second proximate samples, whereby one of said first estimate and said second estimate, respectively, is incorrect; and   selecting means coupled to said first average estimate generating means, to said second average estimate generating means, and to said control signal generating means for selecting as a replacement signal for said erroneous sample said first estimate when said control signal indicates the presence of a defect in one of said second proximate samples and for selecting said second estimate when said control signal indicates a defect in one of said first proximate samples.   
     
     
       4. Apparatus as recited in claim 3 wherein: said first direction is the vertical direction and said second direction is the horizontal direction.